The invention relates to a system for projecting electrically conductive or semi-conductive black or colored toners directly on to a print media.
Conventional printers using dry toners typically employ electrophotographic components to create and develop the desired image on paper or other print media. In electrophotography, a latent image is created on the surface of a photoconducting material by selectively exposing areas of the surface to light. A difference in electrostatic charge density is thereby created between the exposed and unexposed areas on the surface of the photoconductor. The visible image is developed by electrostatic toners containing pigmented components which are usually dispersed in an insulating binder and transferred to the photoconductor via a toner delivery system. The photoconductor and toner particles are oppositely charged, or have different levels of the same charge, and the toner particles are electrostatically attracted to or repelled from either the exposed or unexposed areas on the surface of the photoconductor. A sheet of paper or an intermediate transfer medium is then given an electrostatic charge opposite that of the toner and passed in close proximity to the photoconductor to attract the toner from the photoconductor on to the paper or intermediate medium in the pattern of the image developed on the photoconductor.
It would be a significant advantage in the use of dry toner printers to project the dry toner from a print head directly on to the paper to form the desired images thereon. This direct projection would eliminate the need for a photoconductor and the associated indirect transfer mechanisms used in conventional electrophotographic printers. It would also be advantageous to use conductive or semi-conductive toners to help reduce the degradation of print quality caused by counter-electrostatic field forces that can act to divert toner trajectories in conventional print mechanisms. Such forces are particularly evident in dry toner color printers. The use of conductive or semi-conductive toners could also reduce or eliminate problems caused by xe2x80x9cwrong signxe2x80x9d toner and make the print process less sensitive to varying levels of paper thickness and resistivity.
Accordingly, it is one object of the invention to project dry toner directly on to paper or other print media and thereby eliminate the need for a photoconductor and the associated indirect transfer mechanisms used in conventional electrophotographic printers.
It is another object to use conductive or semi-conductive toners in a direct projection printing device to help reduce the degradation of print quality caused by counter-electrostatic field forces that divert toner trajectories in conventional print mechanisms, eliminate problems caused by xe2x80x9cwrong signxe2x80x9d toner, and make the print process less sensitive to varying levels of paper thickness resistivity.
It is another object of the invention to provide a new toner projection system that generates a toner cloud within a print head structure and selectively projects toner particles on to paper or other print media.
These and other objects and advantages are achieved by a novel system for projecting conductive or semi-conductive toner directly on to paper or another image receiving member. In one embodiment of the invention, a direct electrostatic projection printing device includes a reference electrode, an orifice plate and a projection control electrode interposed between the reference electrode and the orifice plate. An alternating electric field is generated between the reference electrode and the orifice plate to form a cloud of toner particles between the reference electrode and the orifice plate. An electric field is also generated intermittently between the projection control electrode and the orifice plate to project toner particles through the orifice plate on to a sheet of paper or other image receiving member. In one preferred embodiment, the first electric field is an alternating electric field generated by applying an a.c. voltage to the reference electrode and the orifice plate. The second electric field is generated by intermittently applying a d.c. voltage to the projection control electrode at select intervals to selectively project toner particles through the orifice plate. The system can be configured as a full width printing array that includes a series of projection control electrodes and an array of orifices in the orifice plate. Each projection control electrode is aligned with one or more of the orifices in the orifice plate. A control mechanism is used to selectively and intermittently apply a d.c. voltage to the projection control electrodes to project toner through the orifice plate in a predetermined pattern. The control mechanism may include, for example, a series of switches connected between the projection control electrodes and a source of d.c. projection voltage. Alternatively, a pulse generator, or a series of pulse generators, could be used to control the d.c. voltage applied to the projection electrodes.
The toner projection system summarized above can be combined with conventional printer control components to form a direct projection printer. In this embodiment of the invention, the printer includes a formatter that supplies data representing a desired print image to the print engine. The print engine, which is operatively coupled to the formatter, projects an image directly on to the paper. A paper supply mechanism supplies paper to the print engine and a paper output mechanism outputs the printed pages from the print engine. The print engine includes the projector described abovexe2x80x94a reference electrode, an orifice plate and a projection control electrode interposed between the reference electrode and the orifice plate. Again, alternating electric field is generated between the reference electrode and the orifice plate to form a cloud of toner particles within the projector. An electric field is generated intermittently between the projection control electrode and the orifice plate to project toner particles through the orifice plate on to a sheet of paper to print the desired image according to the data supplied by the formatter.